Geochemical Characteristics and Tectonic Environmental Significance of Siliceous Rocks from Middle Permian Xiala Formation in Chunzhe Area, Xietongmen County, Tibet

Based on field geological survey and main, REE and trace elements analyses, the genesis and geological and tectonic environment of the siliceous rocks from middle Permian Xiala Formation (P₂x)in Chunzhe area, Tibet have been discussed in this paper.The results show that SiO₂ and MgO contents of the siliceous rocks from Chunzhe area have negative correlation.In the double variable diagrams of SiO₂/Al₂O₃-MnO/TiO₂ and Fe₂O₃/FeO-SiO₂/Al₂O₃, they are plotted into the area of hydrothermal sedimentary rocks.The contents of Ag, As and Sb are much higher than the average value of these elements in the crust, and the Ni/Co and Ti/V ratios vary from 0.11 to 2.05 and from 35.90 to 48.37, respectively.The Al/(Al+Fe)ratio and MnO/TiO₂ are relatively low, the values of (La/Yb)_N, (La/Ce)_N and (Ce)_N range from 1.35 to 1.97, from 1.08 to 1.15 and from 0.89 to 0.95, respectively.Combined with mass shallow marine carbonate rocks developed within Xiala formation, the conclusions can be drawn that the siliceous rocks in Chunzhe area was formed in a shallow marine tectonic environment of continental margin, which belong to the hydrothermal sedimentary siliceous rocks related to volcanic activity.The discovery of hydrothermal sedimentary siliceous rocks shows that the volcanic hydrothermal exhalative event should happen at the west Gangdese metallogenic belt in middle Permian.Large lead-zinc polymetallic exhalative deposit had been discovered at Paleozoic Laigu formation in east Gangdise metallogenic belt, which indicate a good prospect to find similar mineral resources in the west Gangdise metallogenic belt.